Many vehicle drivetrains incorporate a continuously variable transmission (CVT) having a drive pulley that is operatively coupled to the engine crankshaft and a driven pulley coupled to a driven shaft. The drive pulley transfers torque to the driven pulley via a drive belt looped around both pulleys.
The drive pulley includes centrifugal actuators, similar to the centrifugal actuator 300 of FIG. 1, through which the drive ratio of the drive pulley is varied progressively as a function of the engine speed. Each centrifugal actuator 300 includes an arm 302 and a roller 304. The drive pulley also includes a movable sheave that is movable axially and a fixed sheave and a housing which are axially fixed. The movable sheave is disposed axially between the housing and the fixed sheave. The fixed sheave, the housing and the movable sheaves are rotatable together. The movable sheave is movable axially toward the fixed sheave by the action of the centrifugal actuators 300 and away from the fixed sheave by a biasing spring. An end 306 of each of the arms 302 of the centrifugal actuators is connected to the movable sheave of the drive pulley by an axle, and pivots outwards about the axle. The rollers 304 are connected to the housing in alignment with the arms 302.
When the arms 302 pivot outwards as a result of centrifugal force, their corresponding rollers 304 roll along the ramp surfaces 312 of the central portions 310 of the arms toward the ends 308 of the arms 302 and the axially movable sheave is pushed towards the fixed sheave.
Although the movable sheave is described as being rotationally fixed relative to the housing and the fixed sheave, there may be some small rotational movement of the movable sheave relative to these parts resulting from manufacturing tolerances and/or wear of the parts. This small relative rotational movement causes the roller 304 and the arm 302 of each centrifugal actuator 300 to move relative to each other in a direction generally parallel to the pivot axis of the arm 302. This relative movement between the roller 304 and the arm 302 causes wear of the outer surface 314 of the roller 304 which can lead to one or more flat spots. Once a flat spot is formed, when the flat spot comes in contact with the ramps surface 312, the roller 304 stops rolling along the ramp surface 312 and slides on this flat spot along the ramp surface 312, thus causing the flat spot to wear even more and get bigger. Thus, as soon as a flat spot appears on the roller 304, the roller 304 is considered worn and is replaced by another roller 304.
Therefore, there is a need for a drive pulley having a centrifugal actuator that does not need to have an element thereof that needs to be replaced as soon as some wear occurs.